The present invention relates to a shift control system having a function for compensating a torque shift specifically generated by a shift operation of a toroidal continuously variable transmission.
Japanese Patent Provisional Publication No. 2001-132827 discloses a torque shift compensation apparatus of a toroidal continuously variable transmission, which apparatus is arranged to compensate a torque shift by controlling a shift control device based on a command gear ratio obtained by adding a desired gear ratio and a torque shift compensation quantity generated at a high-speed side gear ratio. This disclosed apparatus employs one map of the torque shift compensation quantity relative to a transmission input torque and a gear ratio. When one kind of the torque shift compensation quantity is employed as this case, it is common that the torque shift compensation quantity is set so that the compensation of the torque shift is smooth executed in an automatic shift range which is mainly used in the shift ranges.
However, if the torque shift compensation quantity is set to preferably perform in automatic shift range (D-range) although there is a fact that the torque shift compensation quantity varies according to a selected shift range selected from D-range range, other ranges or manual shift mode (M-mode), the torque shift compensation quantity in the other range or the manual mode tends to take excessively large value so that the actual gear ratio deviates from the desired gear ratio.
It is an object of the present invention to provide an improved shift control system which has a function of compensating a torque shift of a toroidal continuously variable transmission according to a selected shift range so as to certainly adjust an actual gear ratio at a desired gear ratio when a shift operation is terminated.
An aspect of the present invention resides in a shift control system of a toroidal continuously variable transmission (toroidal CVT) for a vehicle. The shift control system comprises a controller which is configured to calculate a command gear ratio by adding a desired gear ratio and a torque shift compensation quantity for compensating a difference between the desired gear ratio and an actual gear ratio which difference is generated by a shifting operation of the toroidal CVT, and to set a magnitude of the torque shift compensation quantity employed in an automatic shift range to be larger than a magnitude of the torque shift compensation quantity employed in other shift range except for the automatic shift range when the actual gear ratio is in a first gear ratio region except for a second gear ratio region including a largest gear ratio.
Another aspect of the present invention resides in a method of setting a torque shift compensation quantity employed for compensating a difference between a desired gear ratio and an actual gear ratio which difference is generated by a shifting operation of a toroidal continuously variable transmission (toroidal CVT) for a vehicle, the method comprising the steps of: calculating a command gear ratio by adding the desired gear ratio and the torque shift compensation quantity; and setting a magnitude of the torque shift compensation quantity employed in an automatic shift range to be larger than a magnitude of the torque shift compensation quantity employed in other shift range except for the automatic shift range when the actual gear ratio is in a first gear ratio region except for a second gear ratio region including a largest gear ratio.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.